Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
In operation combustion engines (CEs) repeatedly ignite fuel-air mixtures in an enclosed space thereby generating continuous pulses or flows of extremely hot exhaust. The hot exhaust gases from combustion may be partially cooled during transit along the exhaust line and through various subassemblies integrated into the exhaust line or duct. Those subassemblies may, for example, include an engine gas condition monitoring bay, a catalytic convertor anti-pollution filter and one or more mufflers. The exhaust gases are finally dumped out of the system exhaust outlet(s) at temperatures still well above the boiling point of water—typically 140° C. or more.
This dumping of hot exhaust gas represents, apart from the composition of the exhaust gases, a significant energy wastage by combustion engines when considered in light of the calorific value of the fuel consumed. Engines equipped with a turbocharger harvest a little more of the energy in the flows of engine exhaust gas, but even after pushing the turbine blades of the turbocharger, the exhaust gas carries further energy in the form of heat.
Neither a turbine engine, a jet engine, a 2-stroke nor a 4-stroke engine's power cycles—whether petrol, diesel, aviation or gas-fuelled—is capable of utilising the waste heat remaining in the exhaust gases. In wintertime some of the waste heat can be harvested by a motor vehicle's internal (i.e. passenger cabin) heating system, but in summertime the waste heat may be completely unwanted and thus the waste heat appears principally at the exhaust outlet(s) of the vehicle, with smaller amounts emitted from the engine bulk in all directions by convection, conduction and radiation.